1. Field of the Invention
This invention relates generally to the manipulation and detection of terahertz radiation, and in particular to anti-reflection surfaces suitable for use with terahertz radiation.
2. Description of Related Art
Silicon, especially high resistivity silicon, is widely used in terahertz (THz) components due to its broadband transparent window spanning from microwave to mid-infrared with little absorption of electromagnetic waves. However, because of its inherent high dielectric constant, silicon is usually associated with high Fresnel reflection loss (30% reflectivity in THz power from a single surface) and possibly limiting spectral resolution stemming from the finite time window as a result of secondary reflection from its surfaces. The performance of THz systems can be enhanced by reducing or minimizing the reflection of THz radiation at the air-silicon interface. Reducing reflection can increase dynamic range and improve spectral resolution of THz-based systems.
Anti-reflection (AR) techniques in the visible wavelengths of electromagnetic radiation are well developed. However, in the THz range of the elecrtromangetic spectrum, researchers have yet to identify appropriate materials and material implementation to effectively provide anti-reflection for THz radiation. For example, although high resistivity silicon is a suitable material for a wide range of THz components, such as, windows, filters, and beam splitters, because of silicon's high transparency and low dispersion in the whole THz range, silicon is typically associated with high Fresnel loss due to silicon's high index of refraction. Due to the need to alleviate the high loss and reduce interference, researches have recently attempted to address this need for anti-reflection techniques for THz radiation.
The anti-reflection of electromagnetic radiation waves is typically attempted by single-layer interference designs, absorptive anti-reflection design, inhomogeneous design, and multilayer design. The results of applying these methods and devices have been unsatisfactory. As a result, researches have also attempted to alter the refractive index of materials using a modified structure. For example, silicon “nanotips,” thin metal layers, and surface relief structures have been employed as anti-reflection devices for THz radiation. Typically, these investigations utilize a single-layer design, which is associated with either limited anti-reflection bandwidth or significant insertion loss. However, the present art of THz anti-reflection techniques remain unsatisfactory.
Accordingly, a need persists for a THz anti-reflection device, specifically, a tunable broadband anti-reflection device, having improved broadband anti-reflection functions at THz frequencies, which may be manufactured by conventional fabrication methods.